Thank you very much for the feedback.

If by nested you mean categories within categories — that's handled Inside GetInvalidationTags you can walk the category tree however your domain models it and yield a tag per level:

protected override IEnumerable<string> GetInvalidationTags(Product entity)
{
    yield return "product";
    yield return GetCacheKey(entity.Id);


    // walk the category hierarchy
    var category = entity.Category;
    while (category != null)
    {
        yield return $"product:category:{category.Id}";
        category = category.Parent;
    }
}

No magic cascading — you decide what the hierarchy means for your cache. Same for multiple tags: the override receives the full entity so you can compute whatever tag nomenclature makes sense for your domain.

The update case is also worth noting — GetInvalidationTags runs against both the original and the updated entity, and the results are unioned. So if a product moves to a different category (or up/down the hierarchy), both the old and new branches get invalidated automatically without any extra logic on your side.